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Mach reflection in steady supersonic flow considering wedge boundary-layer correction

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Chinese Journal of Aeronautics 2020年第2期33卷 465-475页

作者： Zijun CHEN Chenyuan BAI Ziniu WU Department of Engineering Mechanics Tsinghua UniversityBeijing 100084China Institute of Aeroengine Tsinghua UniversityBeijing 100084China

Mach reflection in steady supersonic flow is an important phenomenon having received extensive studies,among which simplified theoretical models to predict the size of Mach stem and other flow structure are of particular *** efforts for such models were based on inviscid assumption while in real cases the flow is *** in this paper we consider the influence of wedge boundary layer on the Mach stem *** is done by including a simplified boundary layer model into a recently published inviscid *** this viscous model,the wedge angle and the trailing edge height,which control the Mach stem height,are replaced by their equivalent ones accounting for the displacement effect of the wedge boundary layer,with the boundary layer assumed to be laminar or fully *** viscous model is shown to compare well with numerical results by computational fluid dynamics and gives a Mach stem height as function of the Reynolds number and Mach *** is shown that due to the viscous effect,the Mach stem height is increased,through increasing the effective wedge angle.

关键词： Boundary-layer correction Mach reflection Shock waves Supersonic flow Viscous effect

Recent advances in self-propelled particles

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Science China Chemistry 2017年第10期60卷 1293-1304页

作者： Qi Pan Yan He Department of Chemistry Tsinghua University Beijing 100084 China

"Active" components can be introduced into a passive system to completely change its physical behavior from its typical behavior at thermodynamic equilibrium. To reveal the interaction mechanisms between individuals, researchers have designed unique self-propelled particles to mimic the collective behavior of biological systems. This review focuses on recent theoretical and experimental advances in the study of self-propelled particle systems and their individual and collective behaviors. The potential applications of active particles in chemical, biological and environmental sensing and single particle imaging are discussed.

关键词： self-propelled particles micromotors collective behavior single particle tracking

Cooling and Crystallization of Trapped ^(113)Cd+ Ions for Atomic Clock

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Chinese Physics Letters 2013年第1期30卷 71-74页

作者： WANG Shi-Guang ZHANG Jian-Wei MIAO Kai WANG Zheng-Bo WANG Li-Jun Joint Institute for Measurement Science Tsinghua UniversityBeijing 100084 Department of Physics Tsinghua UniversityBeijing 100084 Department of Precision Instruments and Mechanology Tsinghua UniversityBeijing 100084

We report recent experimental progress toward a trapped ^(113)Cd+ion microwave frequency *** laser cooling,a large number of trapped cadmium ions are cooled to crystallization and the temperature of the ion crystal is measured to be 16±3 *** second order Doppler frequency shift,a main limiting factor of the atomic clock's performance,is estimated to be less than 1×10^(-16).

关键词： limiting microwave crystallization

SEISMIC PROPAGATION SIMULATION IN COMPLEX MEDIA WITH NON-RECTANGULAR IRREGULAR-GRID FINITE-DIFFERENCE

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Acta Mechanica Sinica 2004年第3期20卷 299-306页

作者：孙卫涛杨慧珠 Department of Engineering Mechanics Tsinghua UniversityBeijing 100084China Department of Computer Science & TechnologyTsinghua UniversityBeijing 100084China Department of Engineering Mechanics Tsinghua UniversityBeijing 100084China

This paper presents a finite-difference(FD)method with spatially non-rectangular irregular grids to simulate the elastic wave *** irregular grid finite difference oper- ators with a second-order time and spatial accuracy are used to approximate the velocity-stress elastic wave *** method is very simple and the cost of computing time is not *** geometries like curved thin layers,cased borehole and nonplanar interfaces may be treated with non- rectangular irregular grids in a more flexible *** the multi-grid scheme,this method requires no interpolation between the fine and coarse grids and all grids are computed at the same spatial *** with the rectangular irregular grid FD,the spurious diffractions from'staircase' interfaces can easily be eliminated without using finer *** and stability conditions of the proposed method can be established in a similar form as for the rectangular irregular grid *** Higdon's absorbing boundary condition is adopted to eliminate boundary *** simu- lations show that this method has satisfactory stability and accuracy in simulating wave propagation near rough solid-fluid *** computation costs are less than those using a regular grid and rectangular grid FD method.

关键词： seismic propagation non-rectangular grid finite-difference

Linear Stability of Taylor-Couette Flows with Axial Heat Buoyancy

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Chinese Physics Letters 2006年第8期23卷 2135-2138页

作者：陈建国任玲符松 Center for Public Safety Research Tsinghua University Beijing 100084 Department of Engineering Physics Tsinghua University Beijing 100084 Department of Engineering Mechanics Tsinghua University Beijing 100084

The linear stability is studied of flows confined between two concentric cylinders, in which the radial temperature gradient and axial gravity are considered for an incompressible Newtonian fluid. Numerical method based on the Petrov-Galerkin scheme is developed to deal with the buoyancy term in momentum equations and an additional temperature perturbation equation. Computations of the neutral stability curves are performed for different rotation cases. It is found that the flow instability is influenced by both centrifugal and axial shear instabilities, and the two instability mechanisms interact with each other. The outer cylinder rotation plays dual roles of stabilizer and destabilizer under different rotating stages with the inner cylinder at rest. For the heat buoyancyinduced axial flow, spiral structures are found in the instability modes.

关键词： SHEAR INSTABILITY POISEUILLE FLOW CENTRIFUGAL COMPETITION

Preparation of thermal barrier coatings by ultrasonic plasma spraying

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中国有色金属学会会刊：英文版 2004年第Z1期14卷 92-94页

作者： WEN Xiong-wei LI Lu-ming ZHANG Hua-tang HAO Hong-wei LU Zhi-qing Department of Mechanical Engineering Tsinghua University Beijing 100084 China Department of Mechanical Engineering Tsinghua University Beijing 100084 China Department of Mechanical Engineering Tsinghua University Beijing 100084 China Department of Mechanical Engineering Tsinghua University Beijing 100084 China Department of Mechanical Engineering Tsinghua University Beijing 100084 China

Modulated plasma arc not only can heat the powder, but also can excite ultrasonic of different frequencies and different powers. The principles and characters of the plasma arc-excited ultrasonic were described, and the ultrasonic plasma spraying was compared with normal plasma spraying. Zirconia thermal barrier coatings (TBCs) were fabricated with two kinds of method. The TBCs were studied by the optical microscope observation, SEM observation and bonding strength experiment. The results show that suitable ultrasonic changes the performance and microstructure of TBCs in evidence. And the mechanism of ultrasonic influencing the TBCs was also discussed.

关键词： plasma spraying ultrasonic thermal barrier coatings

PEO-LiClO_4-ZSM5 composite polymer electrolyte(IV):Polarized optical microscopy study

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Science China Chemistry 2005年第6期48卷 574-579页

作者： XI Jingyu QIU Xinping ZHU Wentao CHEN Liquan Department of Chemistry Tsinghua University Beijing 100084 China Department of Chemistry Tsinghua University Beijing 100084 China Department of Chemistry Tsinghua University Beijing 100084 China Department of Chemistry Tsinghua University Beijing 100084 China

Polarized optical microscopy (POM) results show that ZSM5 has great influence on both the nucleation stage and the growth stage of PEO spherulites. Part of ZSM5 particles can act as the nucleus of PEO spherulites and thus increase the amount of PEO spherulites. On the other hand, ZSM5 can restrain the recrystallization tendency of PEO chains through Lewis acid-base interaction and hence decrease the growth speed of PEO spherulites. The increasing amount of PEO spherulites, decreasing size of PEO spherulites, and the incomplete crystalliza-tion are all beneficial for creating more continuous amorphous phases of PEO, which is very important for the transporting of Li+ ions. An adequate amount of ZSM5 can enhance the room temperature ionic conductivity of PEO-LiClO4 based polymer electrolyte for more than two mag-nitudes.

关键词： composite polymer electrolyte, poly (ethylene oxide), ZSM-5, polarized optical microscopy, spherulites.

Hardware Implementation of Spiking Neural Networks on FPGA

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Tsinghua Science and Technology 2020年第4期25卷 479-486页

作者： Jianhui Han Zhaolin Li Weimin Zheng Youhui Zhang the Institute of Microelectronics Tsinghua UniversityBeijing 100084China the Research Institute of Information Technology Tsinghua UniversityBeijing 100084China the Department of Computer Science and Technology Tsinghua UniversityBeijing 100084China

Inspired by real biological neural models,Spiking Neural Networks(SNNs)process information with discrete spikes and show great potential for building low-power neural network *** paper proposes a hardware implementation of SNN based on Field-Programmable Gate Arrays(FPGA).It features a hybrid updating algorithm,which combines the advantages of existing algorithms to simplify hardware design and improve *** proposed design supports up to 16384 neurons and 16.8 million synapses but requires minimal hardware resources and archieves a very low power consumption of 0.477 W.A test platform is built based on the proposed design using a Xilinx FPGA evaluation board,upon which we deploy a classification task on the MNIST *** evaluation results show an accuracy of 97.06%and a frame rate of 161 frames per second.

关键词： Spiking Neural Network(SNN) Field-Programmable Gate Arrays(FPGA) digital circuit low-power MNIST

Real-time frequency transfer system over ground-to-satellite link based on carrier-phase compensation at 10-16 level

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Chinese Physics B 2021年第8期30卷 260-268页

作者： Hui-Jian Liang Shi-Guang Wang Yu Bai Si-Chen Sun Li-Jun Wang Department of Electronic Engineering Tsinghua UniversityBeijing 100084China State Key Laboratory of Precision Measurement Technology and Instruments Tsinghua UniversityBeijing 100084China Department of Precision Instruments Tsinghua UniversityBeijing 100084China Department of Physics Tsinghua UniversityBeijing 100084China

We demonstrate a novel and stable frequency transfer scheme over ground-to-satellite link based on real-time carrier-phase detection and *** performed a zero-baseline measurement with the designed system,an uninterrupted frequency standard signal is recovered in the reception station without additional post-correction of delay error caused in the route,which is because the phase error of the entire route is tracked and compensated continuously in *** achieve this goal,we employed two carriers in the system and the differential signal is transferred in order to eliminate the instability results from the local oscillator at the satellite transponder as well as the common-mode noise induced in the transfer route and microwave *** stability of 3×10^(-16) with an integration time of 1 day was achieved and the time fluctuation during one day was measured to be about±20 *** sources and possible solutions are *** zero-baseline method shows a promising result for real-time satellite-based time and frequency transfer and deserves further research to find whether it works between long-baseline stations.

关键词： frequency transfer ground-to-satellite link carrier-phase compensation